Acute kidney injury in patients undergoing cardiac surgery

The incidence of postoperative acute kidney injury (AKI) in patients undergoing cardiac surgery ranges from 7.7% to 28.1% in different studies, probably in relation to the criteria adopted to define AKI. AKI markedly increases mortality risk. However, despite the development of less invasive techniques, cardiac surgery remains the first option in many conditions such as severe coronary artery disease, valve diseases and complex interventions. The risk of postsurgery AKI can be reduced by adopting less invasive approaches, such as off-pump coronary artery bypass grafting or transcatheter aortic valve implantation, but these options cannot be employed in all cases. Thus, since traditional cardiac surgery remains the only option in many cases, it is important to adopt strategies helping the clinician to prevent AKI or diagnose it early. Old age, preprocedural chronic kidney disease, obesity, some comorbidities, wide pulse pressure and some pharmacological regimens represent risk factors for postsurgery AKI and mortality. Important intraoperative factor are use and duration of cardiopulmonary bypass. Postoperative efforts should be aimed toward maximizing cardiac output, avoiding drugs vasoconstricting the renal artery, providing adequate crystalloid infusion and alkalinizing urine. Fluid management should not be based on the measurements for cardiac filling pressures, which are mostly unreliable in these patients. Novel biomarkers such as cystatin C, kidney injury molecule-1 and human neutrophil gelatinase-associated lipocalin have been found to change earlier than creatinine, particularly when measured in combination, so their use in clinical practice can facilitate early diagnosis and treatment of AKI. The occurrence of oliguria despite adequate cardiovascular therapy can be managed with furosemide, possibly using continuous infusion, or renal replacement therapy.